The invention relates to a laser therapy assembly for revascularization of muscular tissue.
Such assemblies are known and are increasingly finding clinical application, especially in the area of cardiac surgery for the improvement of the vascularization of the cardiac muscle, especially by generating tubular necroses.
In the category of xe2x80x9ctransmyocardial laser revascularizationxe2x80x9d, predominantly three different laser systems, i.e., pulsed CO2 laser, pulsed holmium-YAG laser, and excimer laser are currently used to generate small perforational openings in the heart muscle, for the purpose of remedying blood circulation and supply problems in the affected muscular tissue and stimulating the formation of new vessels mid-to long-term.
Such systems are currently offered by the US companies PLC, CARDIO GENESIS, and USSC. The market prices of these systems are quite expensive.
Although obviously the mechanism which results in the improvement of the supply situation in the cardiac muscle with the use of this system is not yet understood, an at least temporary improvement of the clinical picture is observed in a relatively high percentage of the patients treated. The aforementioned laser systems vary dramatically in their adjustment parameters, with regard to wavelength and the pulse energy applicable and the pulse repetition rate, the pulse width, and the type of application; see in this regard the comprehensive presentation in the book xe2x80x9cTransmyokardiale Laserrevascularization, Stand und Ausblickexe2x80x9d, [Transmyocardial Laser Revascularization, State of the Art and Prospects], volume 11 of the series xe2x80x98Fortschritte in der Lasermedizinxe2x80x99 [Advances in Laser Medicine], ecomed, Landsberg and Munich, 1996.
The object of the invention is to provide a comparatively simple and economical device for revascularization of muscular tissue, especially of cardiac muscular tissue, which offers improved potentials for optimization of the treatment parameters.
The object is accomplished by means of an assembly with the characteristics reported in claim 1.
Surprisingly, it was determined that the outcomes previously achieved with the use of the aforementioned high-energy laser systems could be attributed substantially to two laser-induced effects: (1) the generation of intramuscular shock waves by the process of photoablation of a quick local thermal explosion to vaporize the tissue in the target zone as well as (2) the thermal damage to the marginal zones virtually inevitable, in principle, with this type of laser application, whichxe2x80x94depending on the laser parametersxe2x80x94ranges from coagulation through carbonization to the extreme of hyperthermia.
It has now been possible to demonstrate that the previously reported acute outcomes of this process can be attributed substantially to secondary effects of the shock waves produced and pressure amplitudes associated therewith and that the long-term outcomes can be attributed substantially to the formation of the thermally affected marginal zones of the channels made by the procedure. In the prior art systems used, it is inherently impossible to optimize the action of the shock waves, i.e., the pressure amplitude generated and the duration of the shock as well as the depth of action associated therewith, separately from the marginal thermal damage occurring upon performance of the procedure. It is also impossible to further optimize the acknowledged advantageous formation of a thermal marginal zone separately from the shock waves to produce and optimize the reported long-term outcomes.
The invention includes the technical teaching, building on this knowledge, of adjusting the two effects now generated exclusively by a single laserxe2x80x94shock waves and marginal thermal zonesxe2x80x94independently of each other and optimizing them patient-specifically.
Surprisingly, it further turned out that even ultrasound waves carried by optical fiber, whose basic generation is known from the patent DE-A-4,322,955 A1, can be used to generate the perforation of the muscular tissue necessary to promote vascularization. This is all the more astonishing since the prevailing opinion in the teaching assumes that ultrasound surgical devices can be used exclusively either on parenchymatous or brain tissue and to a limited extent on hard tissue, but not primarily on collagen-containing tissues, such as muscular tissue.
Within the framework of the embodiment of the invention, this problem is solved in that the working frequency of the ultrasound generator is selected in a frequency range between 20 and 100 kHz, preferably in the range between 30 and 50 kHz. Through the use of relatively high frequency ultrasound, even collagen fiber structures such as muscle tissue can be deliberately destroyed; whereby the originally athermal process of ultrasound tissue destruction can deliberately be expanded into a partially thermal process because of the increasing friction on the tissue.
Thus, not only can a fine channel be generated in the myocardium, but this channel can also be provided with an adjustable coagulation zone.
A preferred assembly consists of an either magnetostrictive or piezoelectric ultrasound oscillator, on which an amplitude transformer (a so-called ultrasonic horn) calculated according to prior art is applied to couple the optical fiber. With such a handpiece it is then possible, by application of the ultra-frequent tensile and compressive stresses to the target tissue, to rupture the tissue structure and form channels (bores) in the muscular tissue with roughly the diameter of the sound-conducting optical fiber. By active regulation of the ultrasound frequency, it is thus possible during formation of the bore to deliberately vary the impedance adaptation of the sound transmission between the sound-conducting fiber and tissue, with the result that in the event of erroneous adaptation, excess ultrasonic energy is transferred as friction loss to the channel wall and can be used there for controlled heating and thus to generate the desired marginal thermal zone.
From DE-A4,322,955, it is known that, in principle, the ultrasound oscillator to be used to couple an optical fiber can be provided with a central bore such that laser light can, in principle, also be coupled retrograde into the sound-conducting working fiber in the ultrasound handpiece by providing an additional optical fiber. This capability, which to date has been used exclusively for the transmission of continuous laser light, is now used within the framework of the invention to guide pulses of a Q-switched neodymium-YAG laser simultaneously with the transmission of sound to the distal end of the working fiber. The pulse energy of the Q-switched laser used is set such that an optical perforation can be obtained in the operating field, which results immediately in the generation of shock waves.
It is known that above this optical perforation threshold, the pressure amplitudes of the shock waves can be varied in broad ranges by increasing the laser energy. It is also known that the pulse length of a Q-switched laser can also be varied in broad ranges by active Q-switching, for example, by means of a Pockels cell. However, these measures also assume a completely different applicational aspect in their use within the framework of the invention.
Overall it can be noted that with the assembly mentionedxe2x80x94consisting of an ultrasound transmitter with a working fiber coupled thereto and a pulsed laser beam guided centrally by a Q-switched laserxe2x80x94the intended effects, i.e., the formation of a marginal thermal zone and an effective pressure wave amplitude, can be optimally adjusted separately and independently of each other.